1. Field of the Invention
The present invention relates to static timing analysis, and more particularly to static timing analysis using Miller factors.
2. Description of the Related Art
It is known that static timing analysis can be used to verify timing behavior. Static timing analysis analyzes a circuit design for the earliest and latest possible signal arrival times on each logic path or node within the circuit design, regardless of what is happening along other paths within the circuit. The arrival times combined with the signal transition time (referred to as the slew) are expressed as time windows. Comparing the arrival times at a particular node in the circuit with a required arrival time provides the slack at that node in the circuit. By assuming that the earliest and latest signals as expressed by the time window can be propagated through a particular gate, static timing analysis can be independent of the logic function of the gate.
When performing a static timing analysis, one important consideration is the crosstalk between different signal paths. Crosstalk between signal paths affects the timing of the signal path. Active coupling to a switching node may result in additional delay or reduced delay on that node depending on the direction of switching. If both nodes are switching in the same direction, the delay on both nodes is reduced, whereas if the nodes are switching in opposite directions, the delay is increased.
In known static timing analysis, the effect of this crosstalk is taken into account by calculating a worst case assumption that twice the coupling capacitance is used to capture this opposite direction coupling effect, forming a decoupled version of the circuit for each node, where capacitances are replaced by their Miller equivalent. For example, FIG. 1A, labeled prior art, shows an example of a victim and aggressor signal path. In the example of FIG. 1A, each signal path includes a capacitance to ground (Cg) as well as a cross coupled capacitance (Cc) between the victim signal path and the aggressor signal path. FIG. 1B, labeled prior art, shows an example of signal paths for the victim and aggressor signal in which the victim signal path and the aggressor signal path are decoupled. In the decoupled signal paths, the cross coupled capacitance of each signal path is replaced with a corresponding Miller capacitance (Miller*Cc).